Effective fetch and non-linear four-wave interactions during wave growth in slanting fetch conditions |
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| Authors: | Marcel Bottema Gerbrant van Vledder |
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| Institution: | 1. Institute for Inland Water Management and Waste Water Treatment: Rijkswaterstaat/RIZA PO Box 17, 8200 AA Lelystad The Netherlands;2. Alkyon Hydraulic Consultancy and Research, PO Box 248, 8300 AE Emmeloord The Netherlands;3. Delft University of Technology, P.O. Box 5048, 2600 GA, Delft, The Netherlands |
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| Abstract: | Wave growth in slanting fetch (with wind blowing obliquely off a coast) is investigated with 7 years worth of routine wave measurements in Lake IJssel in The Netherlands and with the SWAN wave model. Two aspects are considered in particular for this case: the validity of the concept of effective fetch and the role of the non-linear four-wave interactions. For slanting and parallel fetch conditions, we found some significant deviations from the effective fetch assumption, leading to 20–35% mismatch in either the peak period Tp or the significant wave height Hm0 respectively. However, the effect of discrepancies between various widely accepted wave growth formulas turned out to be even more important. The wave directions during slanting fetch are significantly ‘steered’ by the coastline, especially in the first kilometre(s) off the coast. The role of the non-linear four-wave interactions is investigated by running the SWAN (version 40.41) wave model with three different quadruplet formulations. Exact quadruplet methods (Xnl) yielded relatively strong wave steering, despite the four-wave interactions being relatively weak. Application of Xnl did not lead to better overall agreement with measurements — improvements for the mean wave period Tm01 were offset by some deterioration for the wave height Hm0. |
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| Keywords: | Waves Wave growth Wave measurements SWAN DIA Xnl |
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